Normal Ultrasound Parameters during the First Trimester

 

Ultrasound Sign

Embryo

Cardiac motion in embryos ³5mm.
Fetal heart rate of above 85 beats per minute.

Yolk sac

Yolk sac <6 mm

Round or spherical

Bright echogenic rim and internal anechoic area

Amnion

Embryo always visualized when amnion is visible

Amniotic fluid

Mean diameter of amniotic cavity is ±10% greater than length of embryo

Gestational sac

³13mm – yolk sac should be visualized
³18mm – embryo should be visualized
Smooth and round on endovaginal scanning

Trophoblastic
Reaction

Regular.
Double decidual reaction.
Trophoblastic reaction above 2mm.
No flow in the intervillous space.

Sac growth

Greater than 0.6mm/day.

bhCG correlation

Direct correlation between sac size and bhCG levels.